Airs – Ian Lance Taylor

Separate Appliances

Why don’t people routinely make appliances which work together? The refrigerator generates heat; this should be routed into the oven. The oven generates heat; this should be routed into the hot water heater. This is probably not significant energy usage compared to cars; is it not worth doing at all?

We need to keep working toward maintaining our lifestyles while minimizing energy inputs. After all, even if we get past oil depletion and excess carbon dioxide, we’ll still eventually have to deal with waste heat.

And why do people still make sinks with separate hot and cold taps, so that you have to middle with them to get the right temperature? A single tap setting the temperature works fine, and is much easier to use in practice. Is this just a style thing, or is there some practical reason for it?

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Ian Lance Taylor

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6 responses to “Separate Appliances”

  1. rwild Avatar
    rwild

    A refrigerator in a warmer environment is less efficient by thermodynamic laws. A single tap in the middle temperature is a fertile ground for some rather nasty bacteria (are they called legionella in English?), whereas the separate taps are too hot or too cold.

  2. Ian Lance Taylor Avatar
    Ian Lance Taylor

    That is interesting, but these problems seem solvable to me.

    Connecting the heat generated by the refrigerator to the oven need not imply putting the refrigerator into a warmer environment. The over should be insulated anyhow. The refrigerator doesn’t have to be adjacent to the oven in order to transfer the heat.

    Many sinks do have a single tap right now. What I wonder about is why people still make sinks with two taps. I’m not suggesting that the single tap generate warm water. I’m suggesting that a single control merge the two water streams, so that the same temperature is always available by setting the control to a single position. This is routine in new showers, is fairly common in new bathtubs, and is available in new sinks. I just don’t understand why anybody would want anything else in a new sink.

  3. rwild Avatar
    rwild

    Unless memory serves me wrong about the operation of heat pumps, it is energetically not favorable to make the hotter area even hotter. But as I understand your suggestion, that’s what would happen: if the heat is not exchanged with the surrounding, but instead with a warmer place (the oven), then the temperature difference between hot and cold area is larger, making the process less efficient.

    As to the taps, I misunderstood you there first. FWIW, I have yet to see a sink in a kitchen or bathroom (in Germany) that has two taps and isn’t 10 or more years old.

    > After all, even if we get past oil depletion and excess carbon dioxide, we’ll still
    > eventually have to deal with waste heat.

    Cogeneration does what you’re suggesting. I think that’s energetically much more sensible than trying to reuse (by complicated techniques) waste heat generated in households. The simple stuff (use oven as radiator) is, well, simple, and hopefully done by people already.

    If you’re suggesting that waste heat have an effect on global warming, then all I heard was that was not nearly the case yet.

  4. Ian Lance Taylor Avatar
    Ian Lance Taylor

    With the refrigerator, I’m suggesting that the heat from the refrigerator be sent to the oven while the oven is off, prewarming it. I’m thinking that that way less energy will be needed when the over is turned on. My refrigerator blows warm air out the bottom, and I was thinking that could be ducted to the over. But you could well be right that that would make the refrigerator less efficient, and therefore is not worth doing.

    The waste heat idea is just an extreme example, for thousands of years in the future.

  5. etbe Avatar
    etbe

    The cooling elements of my fridge seem to be at about 37C (based on how they feel). 37C is not much of an improvement from 20C when you want to bake at 150C.

    What I have been wondering about is whether it would be a benefit to have the fridge cooling elements outside the house. In winter having them outside would give greater efficiency to fridge operation but having the fridge waste heat in the house would be a good thing. In summer having the cooling elements outside would reduce the work of the A/C (or whatever you do to cool your house) but increase the work done by the fridge.

    Of course such a system would be more expensive and difficult to install.

  6. Ian Lance Taylor Avatar
    Ian Lance Taylor

    I agree it’s not much of an improvement, but it seems to me that every little thing helps.

    It might be interesting to be able to switch back and forth between having the cooling elements outside and inside, by redirecting the flow depending on conditions.

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